Mid-infrared light sources are useful in many applications, such as bio sensing, environmental monitoring, homeland security and medical diagnostics. Quantum cascade lasers are often used as such light sources at mid-infrared wavelengths. Commercial tunable quantum cascade lasers are available with an average power that is typically in the range of 10 to 100 mW.
Amplifiers incorporating rare-earth ions are known in the art. Such fiber lasers and amplifiers may be doped with Tb3+, Dy3+ or Pr3+ which possess numerous transitions in the wavelength range from 3-12 μm. A three-level system, by way of example, using a Dy3+ doped chalcogenide fiber laser at 3.3 μm and 4.7 μm is known. As a result of the construction, as known from cascading lasers, there are two separate lasing wavelengths resulting from the emissions spectra of the transitions. For the transition from 6H13/2→6H15/2, the emitted wavelength is ˜3.3 μm, and for the transition from 6H11/2→6H13/2, the emitted wavelength is ˜4.7 μm. These emitted wavelengths do not overlap. As a result, an idler at 3.3 μm is required to depopulate the ions in the excited level, and obtains a slope efficiency of only 16% in output power at a wavelength of 4.7 μm, which is a low efficiency.